The invention relates generally to conveyor belts having electrically conductive sensor loops embedded therein and, more particularly, to a sensor system for a conveyor belt for detecting and locating belt degradation and damage.
In a multitude of commercial applications, it is common to employ a heavy duty conveyor belt for the purpose of transporting product and material. The belts so employed may be relatively long, on the order of miles, and represent a high cost component of an industrial material handling operation. In many applications, the belts are susceptible to damage from the material transported thereby and a rip (slit, cut or tear) may develop within the belt. A torn or ripped belt can be repaired once detected. The cost of repairing a heavy duty conveyor belt and the cost of cleaning up material spilled from the damaged belt can be substantial. If, however, such a rip or tear commences and the belt is not immediately stopped, the rip can propagate for a substantial distance along the belt. It is, therefore, desirable to detect and locate a rip in the belt as quickly as possible after it commences and to immediately terminate belt operation, whereby minimizing the extent of the damage to the belt.
It is well known to employ sensors within conveyor belts as part of a rip detection system. In a typical system, sensors in the form of loops of conductive wire are affixed or embedded in the belt and provide a rip detection utility as part of an overall rip detection system. Rip detection is achieved through the inferential detection of an xe2x80x9copen circuitxe2x80x9d condition in one or more of the sensor loops in the belt. Typically an electrical energy source external to the belt is inductively or capacitively coupled to a sensor loop in the belt. A break in the conductive wire loop of the sensor may be detected by a remote transmitter/receiver (exciter/detector). Disposition of a plurality of such sensors at intervals along the conveyor may be effected with each sensor passing within read range of one or more exciter/detectors at various locations. A rip or tear will encounter and damage a proximal sensor loop and the existence of the tear will be detected when the proximal sensor loop damage is detected as an open circuit by the reader at its next pass. In this manner, the existence of a tear will be promptly detected and repaired and damage to the belt therefrom minimized.
U.S. Pat. No. 3,742,477 (Enabnit; 1973) discloses a xe2x80x9cfigure eightxe2x80x9d sensor loop useful within belt sensor system. U.S. Pat. No. 4,854,446 (Strader; 1989) teaches a xe2x80x9cfigure eightxe2x80x9d sensor loops disposed at intervals along a conveyor belt. U.S. Pat. No. 6,352,149 (Gartland, 2002) provides a system in which antennae are embedded in a conveyor belt to couple with an electromagnetic circuit consisting of two detector heads and an electronic package. Coupling occurs only when an antenna passes across the detector heads and can only occur when the loop integrity has not been compromised.
The subject invention concerns a sensor system for a conveyor belt that facilitates rip detection and location. According to the invention, at least one rip detection sensor is incorporated within a conveyor belt and comprises a conductor formed in an endless loop. A transponder is incorporated within the belt coupled electromagnetically to the conductor loop. The transponder transmits an identification signal responsive to an energizing signal whereby the location of the transponder and its respective loop antenna/sensor along the belt may be ascertained. The responsive identification signal from the transponder is induced into the conductor loop and relayed thereby to a proximate reader/detector. A second reader/detector is mounted at an opposite side of the belt and its function is to monitor the integrity of the conductive loop by detecting or not detecting the presence of the transponder response in the loop. The ID number of the transponder, once received by the reader/detector, is cross-referenced by control logic to recognize the specific physical location of the coupled loop/transponder on the belt. The location on the belt where a rip or tear occurs may thereby be determined.
According to one aspect of invention, the second detector may be employed to monitor the integrity of the conductor loop. The second detector detects the presence or absence of the response identification signal from the transponder in the conductor loop. If the loop is not intact, the signal will not be carried by the loop and the second sensor head will not detect the signal. Non-detection of the response signal denotes an open circuit in the conductor loop, indicative of a rip or tear in the belt at the location of the loop. The control unit in such an event would immobilize the belt via a relay and indicate the location in the belt at which the rip occurred.
According to another aspect of the invention, a redundant transponder may be deployed in coupled association with each conductor loop to maintain operation of the system in the event that the first transponder becomes damaged. Another aspect of the invention is to deploy a second conductor loop concentric with the first conductive loop to maintain the system in an operable state in the event that the first conductor loop breaks from mechanical failure rather than a rip or tear to the belt.
According to another aspect of the invention, the transponder chip may be housed within a package comprising opposed outside layers of reinforcement material and a center layer of elastomeric material. The transponder may be embedded within the elastomeric layer to protect the transponder from external forces acting on the belt.
According to another aspect of the invention, the transponder chip may be configured into an elongate geometry having a longitudinal axis. The chip may be oriented within the conveyor belt transverse to the direction of belt travel to minimize stress forces on the transponder chip. The package in which the chip is incorporated may further include a protrusion to readily facilitate positioning the package relative to the belt in order to achieve the preferred transverse orientation of the chip relative to the direction of belt travel.
According to another aspect of the invention a method is provided for manufacturing a sensor system for a conveyor belt incorporating within it a rip detection sensor comprising at least one conductor formed in an endless loop. The method comprises the steps: providing a transponder coupled with the loop and adapted to transmit an identification signal responsive to an energizing signal; providing a transmitter for transmitting the energizing signal to the transponder; locating a detector adjacent the belt to receive the identification signal from the transponder; providing detection means to detect the presence of a discontinuity in the conductor loop; and providing control means to issue a stop command to immobilize the belt in the event a discontinuity in the conductor loop is detected.
According to the invention, the method may further include providing a redundant transponder and/or a redundant conductor loop. The method may further include embedding the transponder within a layer of elastomeric material and packaging the transponder and the elastomeric material layer between opposite layers of reinforcement material.
According to the invention, the method may further include the step of establishing a preferred orientation of the transponder chip relative to a direction of belt travel.